A primary goal of Project IV is to evaluate a new model of the neurological basis of skilled reading. Converging evidence from a number of neuroimaging studies including our own suggests that the development of skilled word identification in reading is related to the development of a highly organized integration of orthographic, phonological and lexical-semantic features of words involving two consolidated left hemisphere(LH) posterior reading circuits: a dorsal (temporo-parietal) circuit and a ventral (occipito-temporal) circuit. According to our account, the temporo-parietal circuit is associated with rule-based word recognition critical for learning to integrate orthographic with phonological and lexical-semantic features of printed words. In turn the occipito-temporal area constitutes a fast, late developing word identification system which underlies fluent word identification. Within the model, the development of the occipito-temporal circuit depends initially on an adequately functioning temporal-parietal system. The proposed research is aimed at both testing these basic assumptions and refining our account. We examine coding within the ventral system is to understand why it is fact and efficient. Additionally, we examine similarities and differences between major reading circuits with respect to the role of phonological, morphological, and lexical-semantic factors, the change responses of these circuits with adaptive learning and experience, and how individual differences in performance can be understood with respect to individual differences in functional organization of reading. Both imaging and behavioral data will be used to develop a formal connectionist simulation of the neurobiological mechanisms for word identification in reading. Work in Project VI on skill reading and in Project V on reading development will both inform and be informed by this developing neurobiological account.